4f.  £v/ay 


U.  S.  DEPARTMENT  OF  AGRICULTURE, 
'  BUREAU  OF  ENTOMOLOGY— BULLETIN  No.  121. 

L.  O.  HOWARD,  Entomologist  and  Chief  of  Bureau. 


THE  BEHAVIOR  OF  THE  HONEY  BEE 
IN  POLLEN  COLLECTING. 


BY 


D.  B.  CASTEEL,  Ph.  D.; 

Collaborator  and  Adjunct  Professor  of  Zoology, 
University  of  Texas. 


Issued  December  31,  1912. 


I 

O^cumSnt^^pt 

i 

.....               "*n»r* 

U.S.  DEPOSITORY 

WASHINGTON: 

GOVERNMENT  PRINTING  OFFICE. 

1912. 


U.  S.  DEPARTMENT  OF  AGRICULTURE, 
BUREAU  OF  ENTOMOLOGY— BULLETIN  No.  121. 

L.  O.  HOWARD.  Entomologist  and  Chief  of  Bureau. 


THE  BEHAVIOR  OF  THE  HONEY  BEE 
IN  POLLEN  COLLECTING. 


BY 


D.  B.  CASTEEL,  Ph.  D., 

Collaborator  and  Adjunct  Professor  of  Zoology, 
University  of  Texas. 


Issued  December  31,  1912. 


WASHINGTON: 

GOVERNMENT  PRINTING  OFFICE. 

1912. 


BUREAU  OF  ENTOMOLOGY. 

L.  O.  Howard,  Entomologist  and  Chief  of  Bureau. 

C.  L.  Marlatt.  Entomologist  and  Acting  Chief  in  Absence  of  Chief. 

R.  S.  Clifton,  Executive  Assistant. 

W.  F.  Tastet,  Chief  Clerk. 

F.  H.  Chittenden,  in  charge  of  truck  crop  and  stored  product  insect  investigations. 

A.  D.  Hopkins,  in  charge  of  forest  insect  investigations. 

W.  D.  Hunter,  in  charge  of  southern  field  crop  insect  investigations. 

F.  M.  Webster,  in  charge  of  cereal  and  forage  insect  investigations. 
A.  L.  Quaintance,  in  charge  of  deciduous  fruit  insect  investigations. 
E.  F.  Phillips,  in  charge  of  bee  culture. 

D.  M.  Rogers,  in  charge  of  preventing  spread  of  moths,  field  work. 
Rolla  P.  Currie,  in  charge  of  editorial  work. 
Mabel  Colcord,  in  charge  of  library. 

Investigations  in  Bee  Culture. 
E.  F.  Phillips,  in  charge. 

G.  F.  White,  J.  A.  Nelson,  experts. 

G.  S.  Demuth,  A.  H.  McCray,  N.  E.  McIndoo,  apicultural  assistants. 
Pearle  H.  Garrison,  preparator. 
D.  B.  Casteel,  collaborator. 
2 


LETTER  OE  TRANSMITTAL. 


U.  S.  Department  of  Agriculture, 

Bureau  of  Entomology, 
Washington,  D.  C,  September  23,  1912. 
Sir  :  I  have  the  honor  to  transmit  herewith  a  manuscript  entitled 
"  The  Behavior  of  the  Honey  Bee  in  Pollen  Collecting,*'  by  Dr.  Dana 
B.  Casteel,  of  this  bureau.  The  value  of  the  honey  bee  in  cross  pol- 
linating the  flowers  of  fruit  trees  makes  it  desirable  that  exact  infor- 
mation be  available  concerning  the  actions  of  the  bee  when  gathering 
and  manipulating  the  pollen.  The  results  recorded  in  this  manu- 
script are  also  of  value  as  studies  in  the  behavior  of  the  bee  and  will 
prove  interesting  and  valuable  to  the  bee  keeper.  The  work  here 
recorded  was  done  by  Dr.  Casteel  during  the  summers  of  1911  and 
1912  at  the  apiary  of  this  bureau. 

I  recommend  that  this  manuscript  be  published  as  Bulletin  No.  121 
of  the  Bureau  of  Entomology. 

Respectfully,  L.  O.  Howard, 

Entomologist  and  Chief  of  Bureau. 
Hon.  James  Wilson, 

Secretary  of  Agriculture. 


CONTENTS. 


Page. 

Introduction 7 

The  structures  concerned  in  the  manipulation  of  pollen 7 

The  pollen  supply 10 

General  statement  of  the  pollen-collecting  process 11 

Action  of  the  forelegs  and  mouthparts 13 

Action  of  the  middle  legs 14 

Action  of  the  hind  legs 16 

Additional  details  of  the  basket-loading  process 18 

Pollen  moistening 22 

Storing  pollen  in  the  hive 29 

Summary 31 

Bibliography 33 

Index 35 

5 


ILLUSTRATIONS. 


TEXT   FIGURES. 

Page. 
Fig.  1.  Left  foreleg  of  a  worker  bee 8 

2.  Left  middle  leg  of  a  worker  bee 9 

3.  Outer  surface  of  the  left  hind  leg  of  a  worker  bee 10 

4.  Inner  surface  of  the  left  hind  leg  of  a  worker  bee 11 

5.  A  flying  bee,  showing  the  manner  in  which  the  forelegs  and  middle  legs 

manipulate  pollen 14 

6.  A  bee  upon  the  wing,  showing  the  position  of  the  middle  legs  when  they 

touch  and  pat  down  the  pollen  masses 15 

7.  A  bee  upon  the  wing,  showing  the  manner  in  which  the  hind  legs  are 

held  during  the  basket-loading  process 17 

8.  The  left  hind  legs  of  worker  bees,  showing  the  manner  in  which  pollen 

enters  the  basket 19 

9.  Inner  surface  of  the  right  hind  leg  of  a  worker  bee  which  bears  a  com- 

plete load  of  pollen 22 


THE  BEHAVIOR  OF  THE  HONEY  BEE  IN  POLLEN  COLLECTING. 


INTRODUCTION". 

While  working  upon  the  problem  of  wax-scale  manipulation  dur- 
ing the  summer  of  1911  the  writer  became  convinced  that  the  so- 
called  wax  shears  or  pinchers  of  the  worker  honey  bee  have  nothing 
whatever  to  do  with  the  extraction  of  the  wax  scales  from  their 
pockets,  but  rather  that  they  are  organs  used  in  loading  the  pollen 
from  the  pollen  combs  of  the  hind  legs  into  the  corbiculse  or  pollen 
baskets  (Cast eel,  1912).  Further  observations  made  at  that  time  dis- 
closed the  exact  method  by  which  the  hind  legs  are  instrumental  in 
the  pollen-loading  process  and  also  the  way  in  which  the  middle  legs 
aid  the  hind  legs  in  patting  down  the  pollen  masses.  During  the 
summer  of  1912  additional  information  was  secured,  more  particu- 
larly that  relating  to  the  manner  in  which  pollen  is  collected  upon 
the  body  and  legs  of  the  bee,  how  it  is  transferred  to  the  hind  legs, 
how  it  is  moistened,  and  finally  the  method  by  which  it  is  stored  in 
the  hive  for  future  use.  In  the  present  paper  a  complete  account  will 
be  given  of  the  history  of  the  pollen  from  the  time  it  leaves  the  flower 
until  it  rests  within  the  cells  of  the  hive.  The  points  of  more  par- 
ticular interest  in  the  description  of  pollen  manipulation  refer  to 
(1)  the  movements  concerned  in  gathering  the  pollen  from  the 
flowers  upon  the  body  and  legs,  (2)  the  method  by  which  the  baskets 
of  the  hind  legs  receive  the  loads  which  they  carry  to  the  hive,  and 
(3)  the  manner  in  which  the  bee  moistens  pollen  and  renders  it  suf- 
ficiently cohesive  for  packing  and  transportation. 

THE  STRUCTURES  CONCERNED  IN  THE  MANIPULATION  OF 

POLLEN. 

The  hairs  which  cover  the  body  and  appendages  of  the  bee  are  of 
the  utmost  importance  in  the  process  of  pollen  gathering.  For  the 
purposes  of  this  account  these  hairs  may  be  classified  roughly  as 
(1)  branched  hairs  and  (2)  unbranched  hairs,  the  latter  including 
both  long,  slender  hairs  and  stiff,  spinelike  structures. 

Of  these  two  classes  the  branched  hairs  are  the  more  numerous. 
They  make  up  the  hairy  coat  of  the  head,  thorax,  and  abdomen,  with 
the  exception  of  short  sensory  spines,  as  those  found  upon  the  an- 
tenna3 and  perhaps  elsewhere,  and  the  stiff  unbranched  hairs  which 

7 


8 


BEHAVIOR   OF    HONEY   BEE   IN    POLLEN    COLLECTING. 


Trochanter^ 


TMa 


cover  the  surfaces  of  the  compound  eyes  (Phillips,  1905).  Branched 
hairs  are  also  found  upon  the  legs;  more  particularly  upon  the  more 
proximal  segments.  A  typical  branched  hair  is  composed  of  a  long 
slender  main  axis  from  which  spring  numerous  short  lateral  barbs. 
Grains  of  pollen  are  caught  and  held  in  the  angles  between  the  axis 
and  the  barbs  and  between  the  barbs  of  contiguous  hairs.  The  hairy 
covering  of  the  body  and  legs  thus  serves  as  a  collecting  surface  upon 
which  jDollen  grains  are  temporarily  retained  and  from  which  they 
are  later  removed  by  the  combing  action  of  the  brushes  of  the  legs. 
Although,  as  above  noted,  some  unbranched  hairs  are  located  upon 
the  body  of  the  bee.  they  occur  in  greatest  numbers  upon  the  more 
distal  segments  of  the  appendages.  They  are  quite  diverse  in  form, 
some  being  extremely  long  and  slender,  such  as  those  which  curve 

over    the    pollen 
JJoxa  baskets,     others 

being  stout  and 
stiff,  as  those 
which  form  the 
collecting  brushes 
and  the  pecten 
spines. 

The  mouth- 
parts  of  the  bee 
are  also  essential 
to  the  proper  col- 
lection of  pollen. 
The  mandibles 
are  used  to  scrape 
over  the  anthers 
of  flowers,  and 
considerable  pollen  adheres  to  them  and  is  later  removed.  The  same 
is  true  of  the  maxillae  and  tongue.  From  the  mouth  comes  the  fluid 
by  which  the  pollen  grains  are  moistened. 

The  legs  of  the  worker  bee  are  especially  adapted  for  pollen  gath- 
ering. Each  leg  bears  a  collecting  brush,  composed  of  stiff,  un- 
branched hairs  set  closely  together.  These  brushes  are  located  upon 
the  first  or  most  proximal  tarsal  segment  of  the  legs,  known  techni- 
cally as  the  palmae  of  the  forelegs  and  as  the  plantae  of  the  middle 
and  hind  pair.  The  brush  of  the  foreleg  is  elongated  and  of  slight 
width  (fig.  1).  that  of  the  middle  leg  broad  and  flat  (fig.  2).  while 
the  brush  upon  the  planta  of  the  hind  leg  is  the  broadest  of  all.  and 
is  ajso  the  most  highly  specialized.  In  addition  to  these  well-marked 
brushes,  the  distal  ends  of  the  tibia?  of  the  fore  and  middle  legs  bear 
many  stiff  hairs,  which  function  as  pollen  collectors,  and  the  distal 
tarsal  joints  of  all  legs  bear  similar  structures. 


Fig.    1. — Left   foreleg  of  a  worker  bee.      (Original.) 


THE   STRUCTURES   CONCERNED. 


9 


The  tibia  and  the  planta  of  the  hind  leg  of  the  worker  bee  are 
greatly  flattened.  (See  figs.  3.  4.)  The  outer  surface  of  the  tibia  is 
marked  by  an  elongated  depression,  deepest  at  its  distal  end,  and 
bounded  laterally  by  elevated  margins.  From  the  lateral  boundaries 
of  this  depression  spring  many  long  hairs,  some  of  which  arch  over 
the  concave  outer  surface  of  the  tibia  and  thus  form  a  kind  of  recep- 
tacle or  basket  to  which  the  name  corbicula  or  pollen-basket  is  given. 
The  lower  or  distal  end  of  the  tibia  articulates  at  its  anterior  edge  with 
the  planta.  The  remaining  portion  of  this  end  of  the  tibia  is  flat- 
tened and  slightly  concave,  its 


—Coxa 


—Trochanter 


-Brush  on  Planta 


surface  sloping  upward  from 
the  inner  to  the  outer  surface 
of  the  limb.  Along  the  inner 
edge  of  this  surface  runs  a  row 
of  short,  stiff,  backwardly  di- 
rected spines,  from  15  to  21  in 
number,  which  form  the  pec- 
ten  or  comb  of  the  tibia.  The 
lateral  edge  of  this  area  forms 
the  lower  boundary  of  the 
corbicula r  depression  and  is 
marked  by  a  row  of  very  fine 
hairs  which  branch  at  their 
free  ends.  Immediately  above 
these  hairs,  springing  from  the 
floor  of  the  corbicula.  are  found 
7  or  8  minute  spines,  and  above 
them  one  long  hair  which 
reaches  out  over  the  lower  edge 
of  the  basket. 

The  broad,  flat  planta  (meta- 
tarsus or  proximal  tarsal  seg- 
ment of  the  hind  leg)  is  marked 
on  its  inner  surface  by  several 
rows  of  stiff,  distally  directed 
spines  which  form  the  pollen 
combs.  About  12  of  these  transverse  rows  may  be  distinguished, 
although  some  of  them  are  not  complete.  The  most  distal  row,  which 
projects  beyond  the  edge  of  the  planta.  is  composed  of  very  strong, 
stiff  spines  which  function  in  the  removal  of  the  wax  scales  (Casteel, 
1912).  The  upper  or  proximal  end  of  the  planta  is  flattened  and  pro- 
jects in  a  posterior  direction  to  form  the  auricle.  The  surface  of  the 
auricle  is  marked  with  short,  blunt  spines,  pyramidal  in  form,  and  a 
fringe  of  fine  hairs  with  branching  ends  extends  along  its  lateral  edge. 
This  surface  slopes  upward  and  outward. 
61799°— Bull.  121—12 2 


Fig.  2.- 


Left  middle  leg  of  a  worker  bee. 
-inal.) 


10 


uliiawoi;  of   honey  bee  in  pollen  collecting. 


THE  POLLEN   SUPPLY. 


When  bees  collect  pollen  from  flowers  they  may  be  engaged  in  this 
occupation  alone  or  may  combine  it  with  nectar  gathering.  From 
some  flowers  the  bees  take  only  nectar,  from  others  only  pollen;  a 

third  class  of  flowers  furnishes 
an  available  supply  of  both  of 
these  substances.  But  even 
where  both  pollen  and  nectar 
are  obtainable  a  bee  may 
gather  nectar  and  disregard 
the  pollen.  This  is  well  illus- 
trated by  the  case  of  white 
clover.  If  bees  are  watched 
while  working  upon  clover 
flowers,  the  observer  will  soon 
perceive  some  which  bear  pol- 
len masses  upon  their  hind 
legs,  while  others  will  continue 
to  visit  flower  after  flower, 
dipping  into  the  blossoms  and 
securing  a  plentiful  supply  of 
nectar,  yet  entirely  neglecting 
the  pollen. 

The  supply  of  pollen  which 
is  available  for  the  bees  varies 
greatly  among  different  flow- 
ers. Some  furnish  an  abun- 
dant amount  and  present  it  to 
the  bee  in  such  a  way  that 
little  difficulty  is  experienced 
in  quickly  securing  an  ample 
load,  while  others  furnish  but 
little.  When  flowers  are  small 
and  when  the  bee  approaches 
them  from  above,  little,  if  any, 
pollen  is  scattered  over  the 
bee's  body,  all  that  it  acquires 
being  first  collected  upon  the 
mouth  and  neighboring  parts, 
of  a  Very  different  conditions  are 
met  with  when  bees  visit  such 
plants  as  corn  and  ragweed.  The  flowers  of  these  plants  are  pendent 
and  possess  an  abundant  supply  of  pollen,  which  falls  in  showers  over 
the  bodies  of  the  bees   as  they  crawl  beneath  the  blossoms.     The 


%-Planta 


Pig.  ::. 


Outer  surface  of  the  left  hind  le^ 
worker   bee.      (Original.) 


GENERAL   STATEMENT   OF   PROCESS. 


11 


supply  of  pollen  which  lodges  upon  the  body  of  the  bee  will  thus 
differ  considerably  in  amount,  depending  upon  the  type  of  flower 
from  which  the  bee  is  collecting,  and  the  same  is  true  regarding  the 
location  upon  the  body  of  a  bee  of  pollen  grains  which  are  available 
for  storage  in  the  baskets. 
Moreover,  the  movements 
concerned  in  the  collection 
of  the  pollen  from  the  va- 
rious body  parts  of  the 
bee  upon  which  it  lodges 
will  differ  somewhat  in 
the  two  cases,  since  a 
widely  scattered  supply 
requires  for  its  collection 
a ddit ional  movements, 
somewhat  similar  in  na- 
ture to  those  which  the 
bee  employs  in  cleaning 
the  hairs  which  cover  its 
bodv. 


Tibia 


-Anterior 
edge 


Posternr 
eage- 


GENERAL  STATEMENT 
OF  THE  POLLEN-COL- 
LECTING  PROCESS. 


Pecten 


Auricle 


Pollen 
onPlanfa 


A  very  complete  knowl- 
edge of  the  pollen-gather- 
ing behavior  of  the  worker 
honey  bee  may  be  obtained 
by  a  study  of  the  actions 
of  bees  which  are '  work- 
ing upon  a  plant  which 
yields  pollen  in  abun- 
dance. Sweet  corn  is  an 
ideal  plant  for  this  pur- 
pose, and  it  will  be  used 
as  a  basis  for  the  descrip- 
tion which  follows. 

In  attempting  to  out- 
line the  method  by  which  FlG 
pollen  is  manipulated  the 
writer  wishes  it  to  be  understood  that  he  is  recounting  that  which 
he  has  seen  and  that  the  description  is  not  necessarily  complete, 
although  he  is  of  the  opinion  that  it  is  very  nearly  so.  The  move- 
ments of  the  legs  and  of  the  mouthparts  are  so  rapid  and  so  many 


Inner    surface    of    the    left    hind    leg    of    a 
worker  bee.      (Original  ) 


12  BEHAVIOR   OF   HONEY   BEE   IX    POLLEN   COLLECTING. 

members  are  in  action  at  once  that  it  is  impossible  for  the  eye  to 
follow  all  at  the  same  time.  However,  long-continued  observation, 
assisted  by  the  study  of  instantaneous  photographs,  gives  confidence 
that  the  statements  recorded  are  accurate,  although  some  movements 
may  have  escaped  notice. 

To  obtain  pollen  from  corn  the  bee  must  find  a  tassel  in  the  right 
stage  of  ripeness,  with  flowers  open  and  stamens  hanging  from  them. 
The  bee  alights  upon  a  spike  and  crawls  along  it,  clinging  to  the 
pendent  anthers.  It  crawls  over  the  anthers,  going  from  one  flower 
to  another  along  the  spike,  being  all  the  while  busily  engaged  in  the 
task  of  obtaining  pollen.     This  reaches  its  body  in  several  ways. 

As  the  bee  moves  over  the  anthers  it  uses  its  mandibles  and  tongue, 
biting  the  anthers  and  licking  them  and  securing  a  considerable 
amount  of  pollen  upon  these  parts.  This  pollen  becomes  moist  and 
sticky,  since  it  is  mingled  with  fluid  from  the  mouth.  A  considerable 
amount  of  pollen  is  dislodged  from  the  anthers  as  the  bee  moves  over 
them.  All  of  the  legs  receive  a  supply  of  this  free  pollen  and  much 
adheres  to  the  hairs  which  cover  the  body,  more  particularly  to  those 
upon  the  ventral  surface.  This  free  pollen  is  dry  and  powdery  and 
is  very  different  in  appearance  from  the  moist  pollen  masses  with 
which  the  bee  returns  to  the  hive.  Before  the  return  journey  this 
pollen  must  be  transferred  to  the  baskets  and  securely  packed  in  them. 

After  the  bee  has  traversed  a  few  flowers  along  the  spike  and  has 
become  well  supplied  with  free  pollen  it  begins  to  collect  it  from  its 
body,  head,  and  forward  appendages  and  to  transfer  it  to  the  pos- 
terior pair  of  legs.  This  may  be  accomplished  while  the  bee  is 
resting  upon  the  flower  or  while  it  is  hovering  in  the  air  before 
seeking  additional  pollen.  It  is  probably  more  thoroughly  and  rap- 
idly accomplished  while  the  bee  is  in  the  air,  since  all  of  the  legs  are 
then  free  to  function  in  the  gathering  process. 

If  the  collecting  bee  is  seized  with  forceps  and  examined  after  it 
has  crawled  over  the  stamens  of  a  few  floAvers  of  the  corn,  its  legs 
and  the  ventral  surface  of  its  body  are  found  to  be  thickly  powdered 
over  with  pollen.  If  the  bee  hovers  in  the  air  for  a  few  moments 
and  is  then  examined  very  little  pollen  is  found  upon  the  body  or 
upon  the  legs,  except  the  masses  within  the  pollen  baskets.  "While  in 
the  air  it  has  accomplished  the  work  of  collecting  some  of  the  scat- 
tered grains  and  of  storing  them  in  the  baskets,  while  others  have 
been  brushed  from  the  body. 

In  attempting  to  describe  the  movements  by  which  this  result  is 
accomplished  it  will  be  best  first  to  sketch  briefly  the  roles  of  the 
three  pairs  of  legs.    They  are  as  follows : 

(a)  The  first  pair  of  legs  remove  scattered  pollen  from  the  head 
and  the  region  of  the  neck,  and  the  pollen  that  has  been  moistened 
by  fluid  substances  from  the  mouth. 


ACTION   OF   FORELEGS  AND   MOUTHPARTS.  13 

(b)  The  second  pair  of  legs  remove  scattered  pollen  from  the 
thorax,  more  particularly  from  the  ventral  region,  and  they  re- 
ceived the  pollen  that  has  been  collected  by  the  first  pair  of  legs. 

(<?)  The  third  pair  of  legs  collect  a  little  of  the  scattered  pollen 
from  the  abdomen  and  they  receive  pollen  that  has  been  collected 
by  the  second  pair.  Nearly  all  of  this  pollen  is  collected  by  the 
pollen  combs  of  the  hind  legs,  and  is  transferred  from  the  combs  to 
the  pollen  baskets  or  corbicula?  in  a  manner  to  be  described  later. 

It  will  thus  be  seen  that  the  manipulation  of  pollen  is  a  succes- 
sive process,  and  that  most  of  the  pollen  at  least  passes  backward 
from  the  point  where  it  happens  to  touch  the  bee  until  it  finally 
reaches  the  corbicula?  or  is  accidentally  dislodged  and  falls  from  the 
rapidly  moving  limbs. 

ACTION  OF  THE   FORELEGS  AND  MOUTHPARTS. 

Although  the  pollen  of  some  plants  appears  to  be  somewhat  sticky, 
it  ma}'  be  stated  that  as  a  general  rule  pollen  can  not  be  successfully 
manipulated  and  packed  in  the  baskets  without  the  addition  of  some 
fluid  substance,  preferably  a  fluid  which  will  cause  the  grains  to 
cohere.  This  fluid,  the  nature  of  which  will  be  considered  later, 
comes  from  the  mouth  of  the  bee,  and  is  added  to  the  pollen  which 
is  collected  by  the  mouthparts  and  to  that  which  is  brought  into  con- 
tact with  the  protruding  tongue  and  maxilla?,  and,  as  will  appear, 
this  fluid  also  becomes  more  generally  distributed  upon  the  legs  and 
upon  the  ventral  surface  of  the  collecting  bee. 

"When  a  bee  is  collecting  from  the  flowers  of  corn  the  mandibles  are 
actively  engaged  in  seizing,  biting,  and  scraping  the  anthers  as  the 
bee  crawls  over  the  pendent  stamens.  Usually,  but  not  always,  the 
tongue  is  protruded  and  wipes  over  the  stamens,  collecting  pollen 
and  moistening  the  grains  thus  secured.  Some  of  the  pollen  may 
possibly  be  taken  into  the  mouth.  All  of  the  pollen  which  comes  in 
contact  with  the  mouthparts  is  thorough^  moistened,  receiving  more 
fluid  than  is  necessary  for  rendering  the  grains  cohesive.  This 
exceedingly  wet  pollen  is  removed  from  the  mouthparts  by  the  fore- 
legs (fig.  5) j  and  probably  the  middle  legs  also  secure  a  little  of  it 
directly,  since  they  sometimes  brush  over  the  lower  surface  of  the 
face  and  the  mouth.  In  addition  to  removing  the  very  moist  pollen 
from  the  mouth  the  forelegs  also  execute  cleansing  movements  over 
the  sides  of  the  head  and  neck  and  the  anterior  region  of  the  thorax, 
thereby  collecting  upon  their  brushes  a  considerable  amount  of  pollen 
which  has  fallen  directly  upon  these  regions,  and  this  is  added  to  the 
pollen  moistened  from  the  mouth,  thereby  becoming  moist  by  contact. 
The  brushes  of  the  forelegs  also  come  in  contact  with  the  anterior 
breast  region,  and  the  hairs  which  cover  this  area  become  moist  with 
the  sticky  exudation  which  the  forelegs  have  acquired  in  the  process 
of  wiping  pollen  from  the  tongue,  maxillae,  and  mandibles. 


14 


BEHAVIOR   OF   HONEY  BEE   IN   POLLEN   COLLECTING. 


ACTION"  OF  THE  MIDDLE  LEGS. 

The  middle  legs  are  used  to  collect  the  pollen  gathered  by  the 
forelegs  and  mouthparts,  to  remove  free  pollen  from  the  thoracic 
region,  and  to  transport  their  load  of  pollen  to  the  hind  legs,  placing 
most  of  it  upon  the  pollen  combs  of  these  legs,  although  a  slight 
amount  is  directly  added  to  the  pollen  masses  in  the  corbiculse.  Most 
of  the  pollen  of  the  middle  legs  is  gathered  upon  the  conspicuous 
brushes  of  the  first  tarsal  segments  or  plantae  of  these  legs. 

In  taking  pollen  from  a  foreleg  the  middle  leg  of  the  same  side  is  ex- 
tended in  a  forward  direction  and  is  either  grasped  by  the  flexed  fore- 
leg or  rubbed  over  the  foreleg  as  it  is  bent  downward  and  backward. 
In  the  former  movement  the  foreleg  flexes  sharply  upon  itself  until 


Pig.  5. — A  flying  bee,  showing  the  manner  in  which  the  forelegs  and  middle  legs  manipu- 
late pollen.  The  forelegs  are  removing  wet  pollen  from  the  mouthparts  and  face.  The 
middle  leg  of  the  right  side  is  transferring  the  pollen  upon  its  brush  to  the  pollen 
combs  of  the  left  hind  planta.  A  small  amount  of  pollen  has  already  been  placed  in 
the  baskets.      (Original.) 

the  tarsal  brush  and  coxa  nearly  meet.  The  collecting  brush  of  the 
middle  leg  is  now  thrust  in  between  the  tarsus  and  coxa  of  the  fore- 
leg and  wipes  off  some  of  the  pollen  from  the  foreleg  brush.  The, 
middle  leg  brush  is  then  raised  and  combs  down  over  the  flexed  fore- 
leg, thus  removing  additional  pollen  from  the  outer  surface  of  this 
leg.  The  middle  leg  also  at  times  reaches  far  forward,  stroking  down 
over  the  foreleg  before  it  is  entirely  flexed  and  apparently  combing 
over  with  its  tarsal  brush  the  face  and  mouthparts  themselves. 
When  the  middle  leg  reaches  forward  to  execute  any  of  the  above 
movements  the  direction  of  the  stroke  is  outward,  forward,  and  then 
back  toward  the  body,  the  action  ending  with  the  brush  of  the  leg  in 
contact  with  the  long  hairs  of  the  breast  and  with  those  which  spring 


ACTION  OF  MIDDLE  LEGS. 


15 


from  the  proximal  segments  of  the  forelegs  (coxa,  trochanter, 
femur).  As  a  result  of  the  oft-repeatecl  contact  of  the  brushes  of 
the  middle  and  forelegs  with  the  breast,  the  long,  branched  hairs 
which  cover  this  region  become  quite  moist  and  sticky,  since  the 
brushes  of  these  two  pair  of  legs  are  wet  and  the  pollen  which  they 
bear  possesses  a  superabundance  of  the  moistening  fluid.  Any  dry 
pollen  which  passes  over  this  region  and  touches  these  hairs  receives 
moisture  by  contact  with  them.  This  is  particularly  true  of  the  free 
dry  pollen  which  the  middle  pair  of  legs  collect  by  combing  over  the 
sides  of  the  thorax. 

The  pollen  upon  the  middle  legs  is  transferred  to  the  hind  legs  in 
at  least  two  ways.  By  far  the  larger  amount  is  deposited  upon  the 
pollen  combs  which  lie  on  the  inner  surfaces  of  the  plantse  of  the 


Fig.  G. — A  bee  upon  the  wing,  showing  the  position  of  the  middle  legs  when  they  touch 
and  pat  down  the  pollen  masses.  A  very  slight  amount  of  pollen  reaches  the  corbiculas 
through  this  movement.      (Original.) 

hind  legs.  To  accomplish  this  a  middle  leg  is  placed  between  the 
plantse  of  the  two  hind  legs,  which  are  brought  together  so  as  to  grasp 
the  brush  of  the  middle  leg,  pressing  it  closely  between  them,  but 
allowing  it  to  be  drawn  toward  the  body  between  the  pollen  combs 
of  the  two  hind  legs.  (See  fig.  5.)  This  action  results  in  the  trans- 
ference of  the  pollen  from  the  middle-leg  brush  to  the  pollen  combs 
of  the  hind  leg  of  the  opposite  side,  since  the  combs  of  that  leg  scrape 
over  the  pollen-laden  brush  of  the  middle  leg.  This  action  may  take 
place  while  the  bee  is  on  the  wing  or  before  it  leaves  the  flower. 

The  middle  legs  place  a  relatively  small  amount  of  pollen  directly 
upon  the  pollen  masses  in  the  corbiculae.  This  is  accomplished  when 
the  brushes  of  the  middle  legs  are  used  to  pat  down  the  pollen  ma»v-s 
and  to  render  them  more  compact.     (See  fig.  G.)     The  legs  are  used 


16  BEHAVIOK   oi'    HONEY    BSE   IX    POLLEN    COLLECTING. 

for  this  purpose  quite  often  during  the  process  of  Loading  the  baskets, 

and  a  small  amount  of  pollen  is  incidentally  added  to  the  n, 
when  the  brushes  come  into  contact  with  them.  A  misinterpretation 
of  this  action  has  led  some  observers  into  the  erroneous  belief  that 
all  or  nearly  all  of  the  corbicular  pollen  is  scraped  from  the  middle- 
leg  brushes  by  the  hairs  which  fringe  the  sides  of  the  baskets.  The 
middle  legs  do  not  scrape  across  the  baskets,  but  merely  pat  down- 
ward upon  the  pollen  which  is  there  accumulating. 

It  is  also  possible  that,  in  transferring  pollen  from  the  middle  leg 
of  one  side  to  the  planta  of  the  opposite  hind  leg,  the  middle-leg 
brush  may  touch  and  rub  over  the  pecten  of  the  hind  leg  and  thus 
directly  place  some  of  its  pollen  behind  the  pecten  spines.  Such  a 
result  is,  however,  very  doubtful. 

ACTION  OF  THE  HIND  LEGS. 

The  middle  legs  contribute  the  major  portion  of  the  pollen  which 
reaches  the  hind  legs,  and  all  of  it  in  cases  where  all  of  the  pollen 
first  reaches  the  bee  in  the  region  of  the  mouth.  However,  when 
much  pollen  falls  upon  the  body  of  the  bee  the  hind  legs  collect  a 
little  of  it  directly,  for  it  falls  upon  their  brushes  and  is  collected 
upon  them  when  these  legs  execute  cleansing  movements  to  remove 
it  from  the  ventral  surface  and  sides  of  the  abdomen.  All  of  the 
pollen  which  reaches  the  corbiculse,  with  the  exception  of  the  small 
amount  placed  there  by  the  middle  legs  when  they  pat  down  the 
pollen  masses,  passes  first  to  the  pollen  combs  of  the  plantae. 

When  in  the  act  of  loading  pollen  from  the  plantar  brushes  to  the 
corbicula?  the  two  hind  legs  hang  beneath  the  abdomen  with  the  tibio- 
femoral joints  well  drawn  up  toward  the  body.  (See  fig.  7.)  The 
two  plantae  lie  close  together  with  their  inner  surfaces  nearly  parallel 
to  each  other,  but  not  quite,  since  they  diverge  slightly  at  their  distal 
ends.  The  pollen  combs  of  one  leg  are  in  contact  with  the  pecten 
comb  of  the  opposite  leg.  If  pollen  is  to  be  transferred  from  the 
right  planta  to  the  left  basket,  the  right  planta  is  drawn  upward  in 
such  a  manner  that  the  pollen  combs  of  the  right  leg  scrape  over 
the  pecten  spines  of  the  left.  By  this  action  some  of  the  pollen  is 
removed  from  the  right  plantar  combs  and  is  caught  upon  the  outer 
surfaces  of  the  pecten  spines  of  the  left  leg. 

This  pollen  now  lies  against  the  pecten  and  upon  the  flattened 
distal  end  of  the  left  tibia.  At  this  moment  the  planta  of  the  left 
leg  is  flexed  slightly,  thus  elevating  the  auricle  and  bringing  the  auri- 
cular surface  into  contact  with  the  pollen  which  the  pecten  has  just 
received.  By  this  action  the  pollen  is  squeezed  between  the  end  of  the 
tibia  and  the  surface  of  the  auricle  and  is  forced  upward  against  the 
distal  end  of  the  tibia  and  on  outward  into  contact  with  the  pollen 
mass  accumulating  in  the  corbicula.     As  this  act,  by  which  the  left 


ACTION    OF    HIND   LEGS. 


17 


basket  receives  a  small  contribution  of  pollen,  is  being  completed,  the 
right  leg  is  lowered  and  the  pecten  of  this  leg  is  brought  into  contact 
with  the  pollen  combs  of  the  left  planta,  over  which  they  scrape  as 
the  left  leg  is  raised,  thus  depositing  pollen  upon  the  lateral  surfaces 
of  the  pecten  spines  of  the  right  leg.     (See  fig.  7.) 

Right  and  left  baskets  thus  receive  alternately  successive  contribu- 
tions of  pollen  from  the  planta  of  the  opposite  leg.  These  loading 
movements  are  executed  with  great  rapidity,  the  legs  rising  and  fall- 
ing with  a  pump-like  motion.  A  very  small  amount  of  pollen  is 
loaded  at  each  stroke  and  many  strokes  are  required  to  load  the 
baskets  completely. 

If  one  attempts  to  obtain,  from  the  literature  of  apiculture  and 
zoology,  a  knowledge  of  the  method  by  which  the  pollen  baskets 


Fig.  7. — A  bee  upon  the  wing,  showing  the  manner  in  which  the  hind  legs  are  held  during 
the  basket-loading-  process.  Pollen  is  being  scraped  by  the  pecten  spines  of  tbe  right 
leg  from  the  pollen  combs  of  the  left  hind  planta.      (Original.) 

themselves  are  loaded,  he  is  immediately  confused  by  the  diversity  of 
the  .accounts  available.  The  average  textbook  of  zoology  follows 
closely  Cheshire's  (188G)  description  in  which  he  says  that  "the  legs 
are  crossed,  and  the  metatarsus  naturally  scrapes  its  comb  face  on  the 
upper  edge  of  the  opposite  tibia  in  the  direction  from  the  base  of  the 
combs  toward  their  tips.  These  upper  hairs  *  *  *  are  nearly 
straight,  and  pass  between  the  comb  teeth.  The  pollen,  as  removed, 
is  caught  by  the  bent-over  hairs,  and  secured.  Each  scrape  adds  to 
the  mass,  until  the  face  of  the  joint  is  more  than  covered,  and  the 
hairs  just  embrace  the  pellet."  Franz  (190G)  states  that  (translated) 
"  the  final  loading  of  the  baskets  is  accomplished  by  the  crossing  over 
of  the  hind-tarsal  segments,  which  rub  and  press  upon  each  other." 
Many  other  observers  and  textbook  writers  evidently  believed  that 
the  hind  legs  were  crossed  in  the  loading  process. 
61790°— Bull.  121—12 3 


18  BEHAVIOR   OF   HONEY  BEE  IN   POLLEN   COLLECTING. 

On  the  other  hand,  it  is  believed  by  some  that  the  middle  legs  are 
directly  instrumental  in  filling  the  baskets.  This  method  is  indicated 
in  the  following  quotation  from  Fleischmann  and  Zander  (1910) 
(translated)  : 

The  second  pair  of  legs  transfer  the  pollen  to  the  hind  legs,  where  it  is 
heaped  up  in  the  pollen  masses.  The  tibia  of  each  hind  leg  is  depressed  on  its 
outer  side,  and  upon  the  edges  of  this  depression  stand  two  rows  of  stiff  hairs 
which  are  bent  over  the  groove.  The  brushes  of  the  middle  pair  of  legs  rub 
over  these  hairs,  liberating  the  pollen,  which  drops  into  the  baskets. 

A  suggestion  of  the  true  method  is  given  by  Hommell  (190G), 
though  his  statements  are  somewhat  indefinite.  After  describing 
the  method  by  which  pollen  is  collected,  moistened,  and  passed  to 
the  middle  legs  he  states  that  (translated)  "the  middle  legs  place 
their  loads  upon  the  pollen  combs  of  the  hind  legs.  There  the  sticky 
pollen  is  kneaded  and  is  pushed  across  the  pincher  (a  traverse  la 
pince),  is  broken  up  into  little  masses  and  accumulates  within  the 
corbicula.  In  accomplishing  this,  the  legs  cross  and  it  is  the  tarsus 
of  the  right  leg  which  pushes  the  pollen  across  the  pincher  of  the 
left,  and  reciprocally.  The  middle  legs  never  function  directly  in 
loading  the  baskets,  though  from  time  to  time  their  sensitive  ex- 
tremities touch  the  accumulated  mass,  for  the  sake  of  giving  assur- 
ance of  its  position  and  size." 

The  recent  valuable  papers  of  Sladen  (1911,  1912,  «,  &,  c,  d,  and  <?), 
who  was  the  first  to  present  a  true  explanation  of  the  function  of 
the  abdominal  scent  gland  of  the  bee,  give  accounts  of  the  process 
by  which  the  pollen  baskets  are  charged,  which  are  in  close  accord 
with  the  writer's  ideas  on  this  subject.  It  is  a  pleasure  to  be  able  to 
confirm  most  of  Sladen's  observations  and  conclusions,  and  weight  is 
added  to  the  probable  correctness  of  the  two  descriptions  and  in- 
terpretations of  this  process  by  the  fact  that  the  writer's  studies  and 
the  conclusion  based  upon  them  were  made  prior  to  the  appearance 
of  Sladen's  papers  and  quite  independent  of  them.  His  description 
of  the  basket-loading  process  itself  is  so  similar  to  the  writer's  own 
that  a  complete  quotation  from  him  is  unnecessary.  A  few  differences 
of  opinion  will,  however,  be  noted  wThile  discussing  some  of  the  move- 
ments which  the  process  involves.  As  will  later  be  noted,  our  ideas 
regarding  the  question  of  pollen  moistening,  collecting,  and  transfer- 
ence are  somewhat  different. 

ADDITIONAL    DETAILS    OF    THE    BASKET-LOADING    PROCESS. 

The  point  at  wThich  pollen  enters  the  basket  can  best  be  determined 
by  examining  the  corbiculse  of  a  bee  shortly  after  it  has  reached  a 
flower  and  before  much  pollen  has  been  collected.  Within  each 
pollen  basket  of  such  a  bee  is  found  a  small  mass  of  pollen,  which  lies 


ADDITIONAL    DETAILS    OF    BASKET-LOADING    PROCESS. 


19 


along  the  lower  or  distal  margin  of  the  basket.  (See  fig  8,  a.)  It  is 
in  this  position  because  it  has  been  scraped  from  the  planta  of  the 
opposite  leg  b}T  the  pecten  comb  and  has  been  pushed  upward  past 
the  entrance  of  the  basket  by  the  continued  addition  of  more  from 
below,  propelled  by  the  successive  strokes  of  the  auricle.     Closer 


Fig.  8. — Camera  drawings  of  the  left  hind  legs  of  worker  bees  to  show  the  manner  in 
which  pollen  enters  the  basket,  a,  Shows  a  leg  taken  from  a  bee  which  is  just  begin- 
ning to  collect.  It  had  crawled  over  a  few  flowers  and  had  flown  in  the  air  about  five 
seconds  at  the  time  of  capture.  The  pollen  mass  lies  at  the  entrance  of  the  basket, 
covering  over  the  fine  hairs  which  lie  along  this  margin  and  the  seven  or  eight  short 
stiff  spines  which  spring  from  the  floor  of  the  corbicula  immediately  above  its  lower 
edge.  As  yet  the  pollen  has  not  come  in  contact  with  the  one  long  hair  which  rises 
from  the  floor  and  arches  over  tbe  entrance.  The  planta  is  extended,  thus  lowering 
the  auricle  ;  b,  represents  a  slightly  later  stage,  showing  the  increase  of  pollen.  The 
planta  is  flexed,  raising  the  auricle.  The  hairs  which  extend  outward  and  upward  from 
the  lateral  edge  of  the  auricle  press  upon  the  lower  and  outer  surface  of  the  small 
pollen  mass,  retaining  it  and  guiding  it  upward  into  the  basket ;  c,  d,  represent  sligbtly 
later  stages  in  the  successive  processes  by  which  additional  pollen  enters  the  basket. 
(Original.) 

examination  of  the  region  between  the  pecten  and  the  floor  of  the 
basket  itself  shows  more  pollen,  which  is  on  its  way  to  join  that 
already  squeezed  into  the  basket. 

If  the  collecting  bee  is  watched  for  a  few  moments  the  increase  will 
readily  be  noted  and  the  fact  will  be  established  that  the  accumulat- 
ing mass  is  gradually  working  upward  or  proximally  from  the  lower 


20  BEHAVIOR    OF    HONEY   BEE   IN    POLLEN   COLLECTING. 

or  distal  edge  of  the  corbicula  and  is  slowly  covering  the  floor  of  this 
receptacle.  (See  fig*.  8,  &,  c,  and  d.)  In  many  instances  the  suc- 
cessive contributions  remain  for  a  time  fairly  separate,  the  whole 
mass  being  marked  by  furrows  transverse  to  the  long  axis  of  the  tibia. 

Sladen  (1912.  b)  notes  the  interesting  fact  that  in  those  rather 
exceptional  cases  when  a  bee  gathers  pollen  from  more  than  one 
species  of  flowers  the  resulting  mass  within  the  corbicula  will  show 
a  stratification  parallel  to  the  distal  end,  a  condition  which  could 
result  only  from  the  method  of  loading  here  indicated. 

As  the  pollen  within  the  basket  increases  in  amount  it  bulges  out- 
ward, and  projects  downward  below  the  lower  edge  of  the  basket. 
It  is  held  in  position  by  the  long  hairs  which  fringe  the  lateral  sides 
of  the  basket,  and  its  shape  is  largely  determined  by  the  form  of 
these  hairs  and  the  direction  in  which  they  extend.  When  the  basket 
is  fully  loaded  the  mass  of  pollen  extends  laterally  on  both  sides  of 
the  tibia,  but  projects  much  farther  on  the  posterior  side,  for  on  this 
side  the  bounding  row  of  hairs  extends  outward,  while  on  the  anterior 
edge  the  hairs  are  more  curved,  folding  upward  and  over  the  basket. 
As  the  mass  increases  in  thickness  by  additions  from  below  it  is  held 
in  position  by  these  long  hairs  which  edge  the  basket.  They  are 
pushed  outward  and  many  of  them  become  partly  embedded  in  the 
pollen  as  it  is  pushed  up  from  below.  When  the  pollen  grains  are 
small  and  the  whole  mass  is  well  moistened  the  marks  made  by  some 
of  the  hairs  will  be  seen  on  the  sides  of  the  load.  (See  fig.  9,  a.) 
These  scratches  are  also  transverse  in  direction  and  they  show  that 
the  mass  has  been  increased  by  additions  of  pollen  pushed  up  from 
below. 

Even  a  superficial  examination  of  a  heavily  laden  basket  shows 
the  fallacy  of  the  supposition  that  the  long  lateral  fringing  hairs  are 
used  to  comb  out  the  pollen  from  the  brushes  of  either  the  hind  or 
middle  legs  by  the  crossing  of  these  legs  over  the  lateral  edges  of  the 
baskets.  They  are  far  from  sufficiently  stiff  to  serve  this  purpose, 
and  their  position  with  relation  to  the  completed  load  shows  con- 
clusively that  they  could  not  be  used  in  the  final  stages  of  the  loading 
process,  for  the  pollen  mass  has  completely  covered  many  of  them 
and  its  outer  surface  extends  far  beyond  their  ends.  The}7  serve 
merely  to  hold  the  pollen  in  place  and  to  allow  the  load  to  project 
beyond  the  margins  of  the  tibia. 

The  auricle  plays  a  very  essential  part  in  the  process  of  loading 
the  basket.  This  structure  comprises  the  whole  of  the  flattened 
proximal  surface  of  the  planta,  except  the  joint  of  articulation  itself, 
and  it  extends  outward  in  a  posterior  direction  a  little  beyond  the 
remaining  plantar  edge.  The  surface  of  the  auricle  is  covered  over 
with  many  blunt,  short  spines  and  its  lateral  margin  is  bounded  by 
a  row  of  short  rather  pliable  hairs,  branched  at  their  ends.     When 


ADDITIONAL    DETAILS    OF    BASKET-LOADING   PROCESS.  21 

the  planta  is  flexed  the  auricle  is  raised  and  its  surface  approaches 
the  distal  end  of  the  tibia,  its  inner  edge  slipping  up  along  the  pecten 
spines  and  its  outer  hairy  edge  projecting  into  the  opening  which 
leads  to  the  pollen  basket.  (See  fig.  8,  b.)  With  each  upward  stroke 
of  the  auricle  small  masses  of  pollen  which  have  been  scraped  from  the 
plantar  combs  by  the  pecten  are  caught  and  compressed  between  the 
spiny  surface  of  the  auricle  and  the  surface  of  the  tibia  above  it. 
The  pressure  thus  exerted  forces  the  pasty  pollen  outward  and  up- 
ward, since  it  can  not  escape  past  the  base  of  the  pecten,  and  directs 
it  into  the  entrance  to  the  corbicula.  The  outward  and  upward  slant 
of  the  auricular  surface  and  the  projecting  hairs  with  which  the  outer 
edge  of  the  auricle  is  supplied  also  aid  in  directing  the  pollen  toward 
the  basket.  Sladen  (1911)  states  that  in  this  movement  the  weak 
wing  of  the  auricle  is  forced  backward,  and  thus  allows  the  escape  of 
pollen  toward  the  basket  entrance,  but  this  appears  both  doubtful  and 
unnecessary,  since  the  angle  of  inclination  of  the  auricular  surface 
gives  the  pollen  a  natural  outlet  in  the  proper  direction. 

If  the  corbicula  already  contains  a  considerable  amount  of  pollen 
the  contributions  which  are  added  to  it  at  each  stroke  of  the  auricle 
come  in  contact  with  that  already  deposited  and  form  a  part  of  this 
mass,  which  increases  in  amount  by  continued  additions  from  below. 
If,  however,  the  corbicula  is  empty  and  the  process  of  loading  is  just 
beginning,  the  first  small  bits  of  pollen  which  enter  the  basket  must 
be  retained  upon  the  floor  of  the  chamber  until  a  sufficient  amount 
has  accumulated  to  allow  the  long  overcurving  hairs  to  offer  it  effec- 
tive support.  The  sticky  consistency  of  the  pollen  renders  it  likely 
to  retain  contact  with  the  basket,  and  certain  structures  near  the 
entrance  give  additional  support.  Several  small  sharp  spines,  seven 
or  eight  in  number,  spring  from  the  floor  of  the  basket  immediately 
within  the  entrance,  and  the  entire  lower  edge  of  the  corbicula  is 
fringed  with  very  small  hairs  which  are  branched  at  their  ends. 
(See  fig.  3.)  One  large  hair  also  springs  from  the  floor  of  the  basket, 
somewhat  back  from  the  entrance,  which  may  aid  in  holding  the 
pollen,  but  it  can  not  function  in  this  manner  until  a  considerable 
amount  has  been  collected. 

As  the  pollen  mass  increases  in  size  and  hangs  downward  and  back- 
ward over  the  pecten  and  auricle  it  shows  upon  its  inner  and  lower 
surface  a  deep  groove  which  runs  outward  from  the  entrance  to  the 
basket.  (See  fig.  9,  b.)  This  groove  results  from  the  continued  im- 
pact of  the  outer  end  of  the  auricle  upon  the  pollen  mass.  At  each 
upward  stroke  of  the  auricle  its  outer  point  comes  in  contact  with 
the  stored  pollen  as  soon  as  the  mass  begins  to  bulge  backward  from 
the  basket. 

Although  the  process  is  a  rather  delicate  one,  it  is  entirely  pos- 
sible so  to  manipulate  the  hind  legs  of  a  recently  killed  bee  that  the 


22 


BEHAVIOR    OF   HONEY   BEE   IX    POLLEN   COLLECTING. 


-^ct 


corbiculae  of  the  two  legs  receive  loads  of  pollen  in  a  manner  similar 
to  that  above  described.  To  accomplish  this  successful!}*  the  operator 
must  keep  the  combs  of  the  planta?  well  supplied  with  moistened 
pollen.  If  the  foot  of  first  one  leg  and  then  the  other  is  grasped 
with  forceps  and  so  guided  that  the  pollen  combs  of  one  leg  rasp  over 
the  pecten  spines  of  the  other,  the  pollen  from  the  combs  will  be 
transferred  to  the  corbicula?.     To  continue  the  loading  process  in  a 

proper  manner,  it  is  also  nec- 
essary to  flex  the  planta  of 
each  leg  just  after  the  pollen 
combs  of  the  opposite  leg 
have  deposited  pollen  behind 
the  pecten.  By  this  action 
the  auricle  is  raised,  com- 
pressing the  pollen  which 
the  pecten  has  secured,  and 
forcing  some  upward  into 
the  corbicula.  Bees'  legs 
which  have  been  loaded  in 
this  artificial  manner  show 
pollen  masses  in  their  cor- 
bicula^ which  are  entirely 
similar  in  appearance  to 
those  formed  by  the  labors 
of  the  living  bee.  More- 
over, by  the  above  method 
of  manipulation  the  pollen 
appears  first  at  the  bottom 
of  the  basket,  along  its  lower 
margin,  gradually  extends 
upward  along  the  floor  of 
the  chamber,  comes  in  con- 
tact with  the  overhanging 
hairs,  and  is  shaped  by  them 
in  a  natural  manner.  All 
attempts  to  load  the  baskets 
by  other  movements,  such  as 
crossing  the  hind  legs  and 
scraping  the  plantar  combs  over  the  lateral  edges  of  the  baskets, 
give  results  which  are  entirely  different  from  those  achieved  by  the 


Fig.  0. — Inner  surface  of  the  right  hind  leg  of  a 
worker  bee  which  bears  a-  complete  load  of 
pollen,  a,  Scratches  in  the  pollen  mass  caused 
by  the  pressure  of  the  long  projecting  hairs 
of  the  basket  upon  the  pollen  mass  as  it  has 
been  pushed  up  from  below  ;  b,  groove  in  the 
pollen  mass  made  bjT  the  strokes  of  the  auricle 
:is  the  mass  projects  outward  and  backward 
from   the  basket.      (Original.) 


living  bee. 


POLLEN   MOISTENING. 


Many  descriptions  have  been  written  by  others  of  the  method  by 
which  pollen  is  gathered  and  moistened.  Some  of  these  are  indefi- 
nite, some  are  incorrect,  while  others  are.  in  part,  at  least,  similar 


POLLEN    MOISTENING.  23 

to  my  own  interpretation  of  this  process.     A  few  citations  will  here 
be  given : 

The  bee  first  strokes  the  head  and  the  proboscis  with  the  brushes  of  the 
forelegs  and  moistens  these  brushes  with  a  little  honey  from  the  proboscis,  so 
that  with  later  strokes  all  of  the  pollen  from  the  head  is  collected  upon  these 
brushes.  Then  the  middle-leg  brushes  remove  this  honey-moistened  pollen  from 
the  forelegs  and  they  also  collect  pollen  from  the  breast  and  the  sides  of  the 
thorax. — [Translation  from  Alefeld,  1861.] 

In  his  account  of  the  basket-loading  process  Alefeld  assigns  to 
the  middle-leg  brushes  the  function  of  assembling  all  of  the  pollen, 
even  that  from  the  plantar  combs,  and  of  placing  it  on  the  corbicula?, 
this  latter  act  being  accomplished  by  combing  over  the  hairy  edge  of 
each  basket  with  the  middle-leg  brush  of  the  same  side. 

It  appears  probable  that  the  bee  removes  the  pollen  from  the  head,  breast, 
and  abdomen  by  means  of  the  hairy  brushes  which  are  located  upon  the  medial 
sides  of  the  tarsal  segments  of  all  of  the  legs,  being  most  pronounced  upon  the 
hind  legs.  The  pollen  is  thus  brought  together  and  is  carried  forward  to  the 
mouth,  where  it  is  moistened  with  saliva  and  a  little  honey. —  [Translation  from 
Franz,  1906.] 

Franz  then  says  that  this  moistened  pollen  is  passed  backward  and 
loaded. 

Since  the  pollen  of  many  plants  is  sticky  and  moist  it  adheres  to  the  surface 
of  the  basket.  Dry  pollen  is  moistened  by  saliva,  so  that  it  also  sticks, — 
[Translation  from  Fleischmann  and  Zander.  1910.] 

Pollen  is  taken  from  flowers  principally  by  means  of  the  tongue,  but  at  times, 
also,  by  the  mandibles,  by  the  forelegs,  and  middle  legs.  The  brushes  of  the 
hind  legs  also  load  themselves,  collecting  from  the  hairs  of  the  body.  The  pollen 
dust  thus  gathered  is  always  transmitted  to  the  mouth,  where  it  is  mixed  with 
saliva. —  [Translation  from  Hommell,  1906.] 

Sladen  considers  the  question  of  how  pollen  is  moistened  by  the 
honey  bee.  bumblebee  ( bumblebee) ,  and  some  other  bees,  but  does  not 
appear  to  reach  definite  conclusions.  In  one  of  his  papers  (1912.  c) 
he  states  that  the  pollen  of  some  plants  may  be  found  in  the  mouth 
cavity  and  in  the  region  of  the  mouth,  but  he  reaches  the  conclusion 
that  this  pollen  is  comparatively  "  dry,''  using  the  word  in  a  "  rela- 
tive sense."  He  asserts  that  "  nowhere  but  on  the  corbicula  and 
hind  metatarsal  brushes  did  I  find  the  sticky  pollen,  except  some- 
times on  the  tips  of  the  long,  branched  hairs  on  the  back  (upper) 
edges  of  the  tibiae  and  femora  of  the  middle  legs,  and  then  only 
in  heavily  laden  bees,  where  it  is  reasonable  to  suppose  it  had 
collected  accidentally  as  the  result  of  contact  with  the  hind  metatarsal 
brushes." 

These  and  other  considerations  lead  Sladen  to  think  that,  in  the 
case  of  the  bumblebee  at  least,  the  pollen  "  may  be  moistened  on  the 
hind  metatarsus  with  the  tongue."  He  states  that  the  tongue  of 
the  bumblebee  is  of  sufficient  leno'th  to  reach  the  hind  metatarsus 


24  BEHAVIOR    OF    HONEY    BEI.    TX    POLLEN    COLLECTING. 

(planta)  and  that  it  might  rub  over  the  brushes  of  the  metatarsi 
or  be  caught  between  them  when  they  are  approximated  and  thus 
moisten  the  two  brushes  simultaneously.  However,  he  has  never 
seen  the  tongue  of  the  collecting  honey  bee  brought  near  to  the  hind 
legs,  and  it  appears  probable  to  him  that  it  can  not  easily  reach  them. 
"  Possibly  the  middle  or  front  legs  are  used  as  agents  for  conveying 
the  honey"  (in  the  case  of  the  honey  bee).  "In  the  humblebee  the 
tongue  is  longer,  and  it  could  more  easily  moisten  the  hind  legs  in 
the  way  suggested." 

In  an  earlier  paper  Sladen  (1912,  a)  gives  the  following  as  his 
opinion  of  the  "  way  in  which  pollen  dust  is  moistened  with  nectar," 
although  he  states  that  this  is  one  of  the  points  "  which  still  remains 
obscure  " : 

The  only  satisfactory  manner  in  which,  it  seems  to  me,  this  can  be  done  is 
for  the  tongue  to  lick  the  tarsi  or  metatarsi  of  the  forelegs,  which  are  covered 
with  stiff  bristles,  well  suited  for  holding  the  nectar,  the  nectar  being  then 
transferred  to  the  metatarsal  brushes  on  the  middle  legs,  and  from  these,  again, 
to  the  metatarsal  brushes  on  the  hind  legs.  The  latter  being  thus  rendered 
sticky,  the  pollen  dust  would  cling  to  them.  The  different  pairs  of  legs  were 
certainly  brought  together  occasionally,  but  not  after  every  scrape  of  the 
hind  metatarsi,  and  their  movements  were  so  quick  that  it  was  impossible 
to  see  what  was  done.  Still,  several  pollen-collecting  bees  that  I  killed  had  the 
tarsi  and  metatarsi  of  the  forelegs  and  the  metatarsal  brushes  of  the  middle 
and  hind  legs  moistened  with  nectar,  and  I  think  it  probable  that  the  moisten- 
ing process,  as  outlined,  is  performed,  as  a  rule,  during  the  flight  from  flower 
to  flower. 

Sladen  (1912,  c)  also  considers  the  possibility  that  the  fluid  which 
moistens  the  pollen  might  be  secreted  through  the  comb  at  the  end 
of  the  tibia,  through  the  tibio-tarsal  joint,  or  from  the  surface  of  the 
auricle,  but  finds  no  evidence  of  glandular  openings  in  these  regions. 
A  suggestion  of  a  similar  nature,  apparently  unknown  to  Sladen, 
was  made  by  T\Tolff  (1873),  who  describes  "sweat-glands"  which, 
he  claims,  are  located  within  the  hind  tibia  and  the  planta,  and 
wrhich  pour  a  secretion  upon  the  surface  of  the  corbicula  and  upon 
the  upper  end  of  the  planta  through  many  minute  openings  located 
at  the  bases  of  hairs,  particularly  those  which  arise  from  the  lateral 
margins  of  the  corbicula.  Wolff  is  convinced  that  the  fluid  thus 
secreted  is  the  essential  cohesive  material  by  which  the  grains  of 
pollen  are  bound  together  to  form  the  solid  mass  which  fills  each 
fully  loaded  basket.  He  noticed  that  the  mouthparts  are  used  to 
collect  pollen,  and  that  some  of  it  is  moistened  with  "  honey  "  or 
"  nectar,"  but  he  does  not  consider  that  the  fluid  thus  supplied  is 
sufficient  to  explain  adequately  the  facility  with  which  the  collecting 
bee  brings  together  the  scattered  grains  of  pollen  and  packs  them 
away  securely  in  the  baskets.  Wolff's  description  of  the  basket-load- 
ing process  itself  is  strikingly  similar  to  that  advocated  later  b}' 
Cheshire. 


POLLEN    MOISTENING.  25 

The  writer  is  not  prepared  to  deny  the  possibility  that  the  surface 
of  the  chitin  of  the  hind  legs  of  worker  bees  may  be  moistened  by 
the  secretion  of  glands  which  lie  beneath  it,  but  he  is  convinced  that 
any  fluid  thus  secreted  bears  little  or  no  relation  to  the  cohesion  of 
the  pollen  grains  within  the  baskets.  Sections  and  dissected  prepa- 
rations of  the  hind  legs  of  worker  bees  show  certain  large  cells  which 
lie  within  the  cavity  of  the  leg  and  which  may  function  as  secreting 
gland  cells;  but  similar  structures  occur  in  even  greater  numbers 
within  the  hind  legs  of  the  drone  and  they  are  found  within  the  hind 
legs  of  the  queen. 

As  has  been  noted,  the  extreme  moisture  of  the  plantar  combs  and 
of  the  tibio-tarsal  articulation  of  the  hind  leg  is  readily  understood 
when  one  recalls  the  manner  in  which  moist  pollen  is  compressed 
between  the  auricle  and  the  tibial  surface  above  it. 

From  the  account  already  given  it  is  evident  that,  in  the  opinion 
of  the  writer,  the  mouth  is  the  source  from  which  the  pollen-moisten- 
ing fluid  is  obtained.  It  is  extremely  difficult  to  determine  with 
absolute  accuracy  the  essential  steps  involved  in  the  process  of  adding 
moisture  to  the  pollen.  In  an  endeavor  to  solve  this  problem  the 
observer  must  of  necessity  consider  a  number  of  factors,  among  which 
may  be  noted  (1)  the  location  upon  the  body  of  the  collecting  bee 
of  "  moist  "  and  of  comparatively  "  dry  "  pollen,  (2)  the  movements 
concerned  in  the  pollen-gathering  and  pollen-transferring  processes, 
(3)  the  relative  moisture  of  those  parts  which  handle  pollen,  (4)  the 
chemical  differences  between  the  natural  pollen  of  the  flower  and 
that  of  the  corbiculse  and  of  the  cells  of  the  hive,  and  (5)  the  observer 
must  endeavor  to  distinguish  between  essential  phenomena  and  those 
which  are  merely  incidental  or  accidental. 

In  the  first  place  it  should  be  noted  that  the  relative  dampness  of 
pollen  within  the  corbiculse  depends  very  largely  upon  the  character 
of  the  flower  from  which  the  pollen  grains  are  gathered.  When 
little  pollen  is  obtained  it  is  much  more  thoroughly  moistened,  and 
this  is  particularly  true  in  cases  when  the  pollen  is  all,  or  nearly  all, 
collected  in  the  region  of  the  mouth,  the  forelegs,  and  head.  When 
a  bee  takes  pollen  from  white  or  sweet  clover  practically  all  of  it 
first  touches  the  bee  in  these  regions.  It  immediately  becomes  moist, 
and  in  this  condition  is  passed  backward  until  it  rests  within  the 
baskets.  There  is  here  no  question  of  "dry"  and  "wet"  pollen, 
or  of  collecting  movements  to  secure  dry  pollen  from  other  regions 
of  the  body,  or  of  the  ultimate  method  by  which  such  free,  dry  pol- 
len becomes  moist. 

The  sticky  fluid  which  causes  pollen  grains  to  cohere  is  found  upon 
all  of  the  legs,  in  the  region  of  their  brushes,  although  the  pollen 
combs  and  auricles  of  the  hind  legs  are  likely  to  show  it  in  greatest 
abundance,  since  nearly  all  of  the  pollen  within  each  basket  has 


26  BEHAVIOR    OF    HONEY   BEE   IN    POLLEN    COLLECTING. 

passed  over  the  auricle,  has  been  pressed  upward  and  squeezed  be- 
t  ween  the  auricle  and  the  end  of  the  tibia  and  the  pollen  mass  above, 
and  by  this  compression  has  lost  some  of  its  fluid,  which  runs  down 
over  the  auricle  and  onto  the  combs  of  the  planta.  It  is  not  necessary 
to  invoke  any  special  method  by  which  these  areas  receive  their 
moisture.  The  compressing  action  of  the  auricle  squeezing  heavily 
moistened  pollen  upward  into  the  basket  is  entirely  sufficient  to 
account  for  the  abundance  of  sticky  fluid  found  in  the  neighborhood 
of  each  hind  tibio-tarsal  joint.  As  has  been  noted,  the  brushes  of 
the  forelegs  acquire  moisture  directly  by  stroking  over  the  proboscis 
and  by  handling  extremely  moist  pollen  taken  from  the  mouthparts. 
The  middle-leg  brushes  become  moist  by  contact  with  the  foreleg  and 
hind-leg  brushes,  probably  also  by  touching  the  mouthparts  them- 
selves, and  by  passing  moist  pollen  backward.  The  hairy  surface  of 
the  breast  is  moistened  by  contact  with  the  fore  and  mid  leg  brushes 
and  with  the  moist  pollen  which  they  bear. 

The  problem  of  the  method  of  pollen  moistening  is  somewhat  more 
complicated  in  the  case  of  flowers  which  furnish  an  excessive  supply. 
ruder  such  conditions  the  entire  ventral  surface  of  the  collecting  bee 
becomes  liberally  sprinkled  with  pollen  grains  which  either  will  be 
removed  and  dropped  or  will  be  combed  from  the  bristles  and  branch- 
ing hairs,  kneaded  into  masses,  transferred,  and  loaded.  The  ques- 
tion naturally  arises  whether  the  movements  here  are  the  same  as 
when  the  plant  yields  but  a  small  amount  of  pollen  which  is  collected 
by  the  mouthparts  and  anterior  legs.  In  the  opinion  of  the  writer 
they  are  essentially  the  same,  except  for  the  addition  of  cleansing 
movements,  executed  chiefly  by  the  middle  and  hind  legs  for  the  col- 
lection of  pollen  which  has  fallen  upon  the  thorax,  upon  the  abdomen, 
and  upon  the  legs  themselves.  Indeed  it  is  questionable  as  to  just 
how  much  of  this  plentiful  supply  of  free  pollen  is  really  used  in 
forming  the  corbicular  masses.  "Without  doubt  much  of  it  falls  from 
the  bee  and  is  lost,  and  in  cases  where  it  is  extremely  abundant  and 
the  grains  are  very  small  in  size  an  appreciable  amount  still  remains 
entangled  among  the  body-hairs  when  the  bee  returns  to  the  hive. 
Yet  it  is  also  evident  that  some  of  the  dry  pollen  is  mingled  with  the 
moistened  material  which  the  mouthparts  and  forelegs  acquire  and 
together  with  this  is  transferred  to  the  baskets. 

In  all  casas  the  pollen-gathering  process  starts  with  moist  pollen 
from  the  mouth  region.  This  pollen  is  passed  backward,  and  in  its 
passage  it  imparts  additional  moisture  to  those  body  regions  which 
it  touches,  the  brushes  of  the  fore  and  middle  legs,  the  planta?  of  the 
hind  legs,  and  the  hairs  of  the  breast  which  are  scraped  over  by  the 
fore  and  middle  leg  brushes.  This  moist  pollen,  in  its  passage  back- 
ward, may  also  pick  up  and  add  to  itself  grains  of  dr}'  pollen  with 
wThich  it  accidentally  comes  in  contact.    Some  of  the  free,  dry  pollen 


POLLEN    MOISTENING.  27 

which  falls  upon  the  moist  brushes  or  upon  the  wet  hairs  of  the 
thorax  is  also  dampened.  Some  of  the  dry  pollen  which  is  cleaned 
from  the  body  by  the  action  of  all  of  the  legs  meets  with  the  wet- 
brushes  or  with  the  little  masses  of  wet  pollen  and  itself  becomes  wet 
by  contact.  Pollen  grains  which  reach  the  corbiculse  either  dry  or 
but  slightly  moistened  are  soon  rendered  moist  by  contact  with  those 
already  deposited.  Little  pollen  gets  by  the  sticky  surfaces  of  the 
combs  of  the  plantar  or  past  the  auricles  without  becoming  thoroughly 
moist. 

Sladen  (1912,  c)  very  aptly  compares  the  mixture  of  dry  pollen 
with  wet  to  the  kneading  of  wet  dough  with  dry  flour  and  suggests 
that  the  addition  of  dry  pollen  may  be  of  considerable  advantage, 
since  otherwise  the  brushes,  particularly  those  of  the  hind  legs, 
would  become  sticky,  "  just  as  the  board  and  rolling  pin  get  sticky 
in  working  up  a  ball  of  dough  if  one  does  not  add  flour.1'  The  addi- 
tion of  a  considerable  amount  of  dry  pollen  gives  exactly  this  result, 
for  the  corbiculse  then  rapidly  become  loaded  with  pollen  mixed 
with  a  minimum  supply  of  moisture  and  the  brushes  remain  much 
dryer  than  would  otherwise  be  the  case.  However,  if  too  much  dry 
pollen  is  added  the  resulting  loads  which  the  bees  carry  back  to  the 
hives  are  likely  to  be  irregular,  for  the  projecting  edges  of  the  masses 
may  crumble  through  lack  of  a  sufficient  amount  of  the  cohesive 
material  by  which  the  grains  are  bound  together. 

On  the  other  hand,  it  does  not  appear  at  all  necessary  to  mix  much 
dry  pollen  with  the  wet,  nor  do  the  brushes  become  sufficiently 
"  sticky  "  from  the  presence  of  an  abundance  of  the  moistening  fluid 
to  endanger  their  normal  functional  activity.  I  have  observed  bees 
bringing  in  pollen  masses  which  were  fairly  liquid  with  moisture, 
and  the  pollen  combs  also  were  covered  with  fluid,  yet  the  baskets 
were  fully  and  symmetrically  loaded. 

Sladen's  different  interpretations  of  the  pollen-moistening  process 
are  rather  confusing,  and  it  is  difficult  to  distinguish  between  what 
he  states  as  observed  facts  and  what  he  puts  forward  as  likely 
hypotheses.  He  agrees  with  me  in  his  observation  that  all  of  the 
legs  become  moist  in  the  region  of  their  brushes  and  also  in  his  sup- 
position that  this  moisture  is  transferred  to  them  from  the  mouth. 
In  this  moistening  process  my  observations  show  that  the  fluid  con- 
cerned is  passed  backward  by  the  contact,  of  the  middle-leg  brushes 
with  the  wet  foreleg  brushes  and  that  the  middle-leg  brushes  in  turn 
convey  moisture  to  the  plantse  as  they  rub  upon  them.  I  am  also 
convinced  that  the  wet  pollen  grains  furnish  additional  moisture  to 
the  brushes  as  they  pass  backward,  and  this  is  particularly  true  in 
the  case  of  the  extremely  moist  surfaces  of  the  auricles  and  the  pollen 
combs  of  the  planta,  since  here  moisture  is  pressed  from  the  pollen 
upon  these  areas.  The  pollen  upon  the  fore  and  middle  leg  brushes 
is  not  always  "  dry  ;'  even  in  "  a  relative  sense." 


28 


BEHAVIOR    OF    HONEY   BEE   IX    POLLEN    COLLECTING. 


In  describing  pollen  manipulation  several  writers  state  that  dry 
pollen  is  picked  up  by  the  brushes  of  the  legs  and  is  carried  forward 
to  the  mouth,  there  moistened  (according  to  some,  masticated),  and 
is  then  carried  backward  by  the  middle  legs  for  loading.  Obviously 
such  accounts  do  not  apply  to  cases  in  which  all  of  the  pollen  is  col- 
lected by  mouthparts  and  forelegs.  Do  they  apply  in  case>  where 
much  pollen  falls  on  the  body  and  limbs?  Without  doubt  a  certain 
amount  of  this  free  pollen  is  brought  forward  when  the  middle  legs, 
bearing  some  of  it,  sweep  forward  and  downward  over  the  forelegs, 
mouthparts,  and  breast.  However,  it  does  not  appear  to  the  writer 
that  this  dry  pollen  is  carried  to  the  mouth  for  the  specific  purpose  of 
moistening  it,  or  that  it  is  essential  to  its  moistening  that  it  be 
brought  in  contact  Avith  the  mouth.  Some  of  it  touches  the  moist 
hairs  on  the  forelegs  and  breast  and  is  moistened  by  contact.  All 
that  remains  on  the  brushes  of  the  middle  legs  secures  moisture  from 
these  brushes  or  from  wet  pollen  which  the  brushes  collect  from  the 
mouthparts  or  forelegs.  The  supposed  necessity  of  carrying  forward 
pollen  to  the  mouth  for  moistening  is  a  delusion.  Some  is  acci- 
dentally brought  forward  and  into  contact  with  the  mouth  and  gets 
wet,  but  the  process  is  not  essential. 

If  the  pollen  which  bees  transport  to  their  hives  has  been  moistened 
wTith  some  fluid  substance  which  causes  the  grains  to  cohere,  this 
addition  should  be  indicated  by  differences  in  the  results  of  an  analy- 
sis of  pollen  from  a  plant  as  compared  with  that  found  in  the  cor- 
bieulse  of  a  bee  which  has  been  working  on  this  plant.  For  the  sake 
of  determining  this  difference  and  in  an  endeavor  to  ascertain,  if 
possible,  the.  approximate  nature  of  the  added  fluid,  analyses  were 
made  of  three  kinds  of  pollen,  as  follows:  (1)  Pollen  collected  by 
hand  from  the  corn  plant  itself;  (2)  pollen  taken  from  the  corbiculse 
of  bees  which  had  secured  their  supply  from  corn;  (3)  pollen  stored 
in  the  cells  of  the  hive.  In  the  first  two  cases  pollen  from  the  same 
species  of  plant  (corn)  was  used.  The  material  from  the  cells  of  the 
hive  was  composed  largely  of  corn  pollen,  but  contained  an  admixture 
of  some  other  pollens. 

The  writer  is  indebted  to  Dr.  P.  B.  Dunbar,  of  the  Bureau  of 
Chemistry,  for  the  following  analyses : 


» 

Pollen 

direct 
from 
corn. 

Corn  pol- 
len from 
corbicula. 

Stored 
pollen 
from 
hive. 

Total  solids                                                        

53.47 

4G.53 
2.87 

'_».  77 
5.79 

66.94 

33.06 

11.07 

3.06 

14.29 

79.66 

20.34 

17.90 

2.25 

Total  reducing  sngai                              

20.  27 

Dry  basis: 

Reducing  sugar 

L37 
5.18 

16.54 
4.57 

22. 47 

2.82 

10.55 

ft 

21.11 

STORING  POLLEN   IN   THE   HIVE.  29 

These  analyses  show  conclusively  that  a  very  large  amount  of 
sugar  has  been  added  to  the  pollen  by  the  time  it  reaches  the  cor- 
biculae.  Calculated  on  a  dry  basis  just  about  twice  as  much  sugar  is 
present  in  the  basket  pollen  as  in  that  from  the  corn  plant.  Xot  only 
is  this  so,  but  the  additional  fact  is  disclosed  that  over  three  times  as 
much  reducing  sugar  is  present  in  the  corbicular  pollen  as  sucrose. 
This  latter  result  indicates  that  honey  (largely  a  reducing  sugar) 
rather  than  nectar  (containing  more  sucrose)  is  the  chief  sugar  in- 
gredient of  the  corbicular  pollen.  The  additional  amount  of  sugar 
(here  again  a  reducing  sugar)  in  the  stored  pollen  of  the  hive  is 
what  might  be  expected,  since  it  is  supposed  that  the  workers  add 
honey  and  possibly  other  ingredients  to  the  pollen  within  the 
storage  cells. 

The  total  solid  percentages,  corn  53.47,  corbicula  66.94,  stored 
pollen  79.66,  also  show  that  the  fluid  substance  which  is  added  is  one 
highly  charged  with  solids,  a  condition  which  honey  amply  fulfills. 

In  the  descriptions  which  have  been  cited  of  the  pollen-gathering 
process  in  which  the  mouth  is  supposed  to  supply  the  requisite  fluid 
three  substances  are  mentioned:  Nectar,  honey,  and  saliva.  The 
analyses  herein  given  indicate  that  reducing  sugar  is  mingled  with 
the  pollen,  and  in  the  case  of  corn  it  is  indicated  that  honey  is  used 
in  greater  abundance.  Without  doubt  a  certain  amount  of  saliva 
also  finds  its  way  to  the  pollen,  but  the  proportion  of  this  substance 
has  not  been  determined.  This  salivary  fluid  may  have  adhesive 
qualities,  but  this  is  scarcely  necessary,  since  honey  alone  is  amply 
sufficient  for  this  purpose. 

It  appears  probable  that  the  fluid  which  a  bee  adds  to  the  pollen 
which  it  is  collecting  varies  somewhat  in  amount,  since  the  pollen  of 
different  plants  differs  considerably  in  moisture  content  and  that  of 
the  same  plant  will  differ  in  this  respect  at  different  times.  Pollen 
collected  in  the  early  morning  before  the  dew  has  left  the  plant  is 
much  more  moist  than  that  found  upon  the  same  plant  later  in  the 
day,  and  the  grains,  if  taken  when  moist,  have  a  natural  tendency  to 
become  aggregated  and  form  small  masses.  Moreover,  this  may  ex- 
plain the  fact  that  bees  make  their  pollen-collecting  trips  during  the 
morning  hours,  rather  than  in  the  afternoon,  although  some  may  be 
seen  upon  the  flowers  throughout  the  whole  day. 

STORING  POLLEN  IN"  THE  HIVE. 

When  the  bee  has  fully  loaded  its  baskets  and  before  it  returns  to 
the  hive  it  often  spends  a  little  time  upon  the  plant  from  which  it 
has  been  collecting,  occupied  with  the  task  of  cleaning  scattered 
grains  of  pollen  from  its  body  and  of  patting  down  securely  the  loads 
which  it  has  obtained.  Upon  its  return  to  the  hive  it  hurries  within 
and  seeks  for  a  suitable  place  in  which  to  deposit  the  pollen.    Some 


30  BEHAVIOR   OP   HONEY  BEE  IN   POLLEN   COLLECTING. 

returning  bees  walk  leisurely  over  the  combs  and  loiter  among  their 
sister  workers,  while  others  appear  to  be  greatly  agitated,  shaking 
their  bodies  and  moving  their  Avings  as  though  highly  excited. 
Many  pollen-bearing  bees  appear  eager  to  receive  food  upon  their 
return  to  the  hive,  and  they  will  solicit  it  from  other  workers  or 
take  it  from  the  honey-storage  cells.  The  workers  of  the  hive  at 
times  take  a  little  of  the  fresh  pollen  from  the  baskets  of  the  laden 
bee,  nibbling  it  off  with  their  mandibles  or  rasping  off  grains  with 
their  tongues. 

If  the  combs  of  a  colony  are  examined,  stored  pollen  will  be  found 
in  various  parts  of  the  hive.  In  the  brood  frames  the  greatest  amount 
is  located  above  and  at  the  sides  of  the  brood  and  between  this  and 
the  stored  honey.  Cells  scattered  through  the  brood  from  which 
young  bees  have  lately  emerged  may  also  contain  pollen.  In  the 
outer  frames  of  the  hive,  where  brood  is  less  likely  to  be  found, 
nearly  all  of  the  cells  may  be  packed  with  pollen,  or  honey-storage 
cells  may  be  found  interspersed  with  those  filled  with  pollen.  As  a 
rule  pollen  is  not  stored  in  drone  comb,  although  this  occasionally 
happens. 

As  the  pollen-bearing  bee  crawls  over  the  combs  it  appears  to  be 
searching  for  a  suitable  cell  in  which  to  leave  its  load.  It  sticks 
the  head  into  cell  after  cell  until  finally  one  is  located  which  meets 
its  requirements,  although  it  is  an  open  question  as  to  why  any  one  of 
a  group  should  be  chosen  rather  than  another.  This  selected  cell 
may  already  contain  some  pollen  or  it  may  be  empty.  If  partly  filled, 
the  pollen  which  it  contains  is  likely  to  be  from  the  same  species  of 
plant  as  that  which  the  bee  carries,  although  different  kinds  of  pollen 
are  often  stored  in  the  same  cell. 

In  preparation  for  the  act  of  unloading  the  bee  grasps  one  edge 
of  the  cell  with  its  forelegs  and  arches  its  abdomen  so  that  the  pos- 
terior end  of  the  abdomen  rests  upon  the  opposite  side  of  the  cell.  The 
body  is  thus  held  firmly  and  is  braced  by  these  two  supports  with  the 
head  and  anterior  thoracic  region  projecting  over  one  of  the  neigh- 
boring cells.  The  hind  legs  are  thrust  down  into  the  cell  and  hang 
freely  within  it,  the  pollen  masses  being  held  on  a  level  with  the  outer 
edge  of  the  cell,  or  slightly  above  it.  The  middle  leg  of  each  side 
is  raised  and  its  planta  is  brought  into  contact  with  the  upper 
(proximal)  end  of  the  tibia  of  the  same  side  and  with  the  pollen  mass. 
The  middle  leg  now  presses  downward  upon  the  pollen  mass,  work- 
ing in  between  it  and  the  corbicular  surface,  so  that  the  mass  is 
shoved  outward  and  downward  and  falls  into  the  cell.  As  the  pollen 
masses  drop,  the  middle  legs  are  raised  and  their  claws  find  support 
upon  the  edge  of  the  cell.  The  hind  legs  now  execute  cleansing  move- 
ments to  remove  small  bits  of  pollen  which  still  cling  to  the  corbicular 


SUMMARY.  31 

surfaces  and  hairs.  After  this  is  accomplished  the  bee  usually  leaves 
the  cell  without  paying  further  attention  to  the  two  pellets  of  pollen 
although  some  collecting  bees  Avill  stick  the  head  into  the  cell,  possi- 
bly to  assure  themselves  that  the  pollen  is  properly  deposited.  It  has 
been  stated  by  some  (Cheshire,  for  example)  that  the  spur  upon  the 
middle  leg  is  used  to  help  pry  the  pollen  mass  from  the  corbicula. 
This  structure  is  in  close  proximity  with  the  mass  while  the  middle 
leg  is  pushing  downward  upon  it,  but  its  small  size  renders  difficult 
an  exact  estimate  of  its  value  in  this  connection.  It  is  certainly  true 
that  the  entire  planta  of  the  middle  leg  is  thrust  beneath  the  upper 
end  of  the  pollen  mass,  but  the  spur  may  be  used  as  an  entering 
wedge. 

Pollen  masses  which  have  been  dropped  by  the  collecting  bee  may 
remain  for  some  time  within  the  cell  without  further  treatment,  but 
usually  another  worker  attends  to  the  packing  of  the  pollen  shortly 
after  it  has  been  deposited.  To  accomplish  this  the  worker  enters  the 
cell  head  first,  seizes  the  pollen  pellets  with  its  mandibles,  breaks 
them  up  somewhat  or  flattens  them  out,  probably  mingles  additional 
fluid  with  the  pollen,  and  tamps  down  the  mass  securely  in  the  bot- 
tom of  the  cell.  As  is  shown  by  the  analyses  of  corbicular  pollen  and 
of  stored  pollen,  certain  substances  are  added  to  the  pollen  after  the 
collecting  bee  leaves  it  in  the  cell.  Sugar  is  certainly  added,  and  it  is 
generally  supposed  that  secretions  from  some  of  the  salivary  glands 
are  mixed  with  the  pollen  after  deposition.  It  appears  probable  that 
the  stored  pollen  or  "  beebread  "  is  changed  somewhat  in  chemical 
composition  through  the  action  of  the  fluids  which  have  been  added 
to  it,  either  during  the  process  of  collection,  at  the  time  of  packing, 
or  later. 

SUMMARY. 

Pollen  may  be  collected  by  the  worker  bee  upon  its  mouthparts, 
upon  the  brushes  of  its  legs,  and  upon  the  hairy  surface  of  its  body. 
When  the  bee  collects  from  small  flowers,  or  when  the  supply  is  not 
abundant,  the  mouthparts  are  chiefly  instrumental  in  obtaining  the 
pollen. 

The  specialized  leg  brushes  of  the  worker  are  used  to  assemble  the 
pollen,  collecting  it  from  the  body  parts  to  which  it  first  adheres  and 
transporting  it  to  the  pollen  baskets  or  corbiculse  of  the  hind  legs.  In 
this  manipulation  the  forelegs  gather  pollen  from  the  mouthparts  and 
head;  the  middle  legs,  from  the  forelegs  and  from  the  thorax;  the 
hind  legs,  from  the  middle  legs  and  from  the  abdomen. 

The  pollen  baskets  are  not  loaded  by  the  crossing  over  of  one  hind 
leg  upon  the  other  or  to  any  great  extent  by  the  crossing  of  the  middle 
legs  over  the  corbiculse.     The  middle  legs  deposit  their  loads  upon  the 


32  BEHAVIOR   OF    HONEY   BEE   IN    POLLEN    COLLECTING. 

pollen  combs  of  the  hind  planta?,  and  the  planta?,  in  turn,  transfer  the 
pollen  of  one  leg  to  the  pecten  comb  of  the  other,  the  pecten  of  one 
leg  scraping  downward  over  the  pollen  comb  of  the  opposite  leg. 
(See  fig.  7.)  A  little  pollen  is  loaded  directly  from  the  middle  legs 
into  the  baskets  when  these  legs  are  used  to  pat  down  the  pollen 
masses.     (See  fig.  6.) 

Aside  from  the  foregoing  exception,  all  of  the  pollen  which  reaches 
the  baskets  enters  them  from  below,  since  it  is  first  secured  by  the 
pecten  combs,  and  is  then  pushed  upward  by  the  impact  of  the 
rising  auricles,  which  squeeze  it  against  the  distal  ends  of  the  tibiae 
and  force  it  on  into  the  baskets  to  meet  that  which  has  gone  before. 

The  long  hairs  which  form  the  lateral  boundaries  of  the  baskets 
are  not  used  to  comb  out  pollen  from  the  brushes  of  any  of  the  legs. 
They  serve  to  retain  the  accumulating  masses  within  the  baskets  and 
to  support  the  weight  of  the  pollen,  as  it  projects  far  beyond  the 
surfaces  of  the  tibia?. 

Pollen  grains  are  moistened  and  rendered  cohesive  by  the  addition 
to  them  of  fluid  substances  which  come  from  the  mouth.  Analyses 
show  that  honey  forms  a  large  part  of  this  moistening  fluid,  although 
nectar  and  secretions  from  the  salivary  glands  are  probably  present 
also. 

In  the  process  of  pollen  manipulation  this  fluid  substance  becomes 
well  distributed  over  the  brushes  of  all  of  the  legs.  The  forelegs 
acquire  moisture  by  brushing  over  the  mouthparts,  and  they  transfer 
this  to  the  hairs  of  the  breast  and  to  the  middle-leg  brushes  when 
they  come  in  contact  with  them.  The  middle-leg  brushes  transmit 
their  moisture  to  the  pollen  combs  of  the  hind  legs  when  they  rub 
upon  them.  All  of  these  brushes  also  transport  wet  pollen  which 
has  come  from  the  mouthparts  and  thereby  acquire  additional  mois- 
ture. The  auricles  and  the  planta?  of  the  hind  legs  become  particu- 
larly wet  from  this  source,  since  fluid  is  squeezed  from  the  wet  pollen 
when  it  is  compressed  between  the  auricles  and  the  distal  ends  of  the 
tibia?.  Dry  pollen  which  falls  upon  the  body  hairs  becomes  moist 
when  brought  into  contact  with  the  wet  brushes  or  with  wet  pollen. 

During  the  process  of  manipulation  pollen  passes  backward  from 
its  point  of  contact  with  the  bee  toward  its  resting  place  within  the 
baskets. 

Pollen  which  the  collecting  bee  carries  to  the  hive  is  deposited  by 
this  bee  within  one  of  the  cells  of  the  comb.  As  a  rule,  this  pollen  is 
securely  packed  in  the  cell  by  some  other  worker,  which  flattens  out 
the  rounded  masses  and  adds  more  fluid  to  them. 


BEHAVIOR  OF   HONEY  BEE  IN   POLLEN   COLLECTING.  33 

BIBLIOGRAPHY. 

Alefeld,  Dr. — Vol.  5.  Nos.  15  and  16.  Eichstadt  Bienen  Zeitung.     Summarized 

in  "Die  Bienenzeitung  in  neuer,  geschichteter  und  systematische  geordneter 

Ausgabe."       Herausgegeben      vom      Schinid     und     Kleine :      Erste     Band, 

Theoretischer  Theile.    1861. 

Casteel,  D.  B.,  1912. — The  manipulation  of  the  wax  scales  of  the  honey  bee, 

Circular  161,  Bureau  of  Entomology,  U.  S.  Dept.  Agriculture,  pp.  15. 
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pp.  [viii]+831. 
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bee.    Proc.  Acad.  Nat.  Sci.  Philadelphia,  vol.  57,  pp.  123-157. 
Sladen,  F.  W.  L.,  1911. — How  pollen  is  collected  by  the  social  bees,  and  the 
part  played  in  the  process  by  the  auricle.     British  Bee  Journal,   vol.  39, 
pp.  491^93,  Dec.  14. 
Sladen,  F.  W.  L.,  1912. —  (a)  How  pollen  is  collected  by  the  honey  bee.    Nature, 
vol.  88,  pp.  586,  587,  Feb.  29. 

1912. —  (&)   Further   notes   on   how    the  corbicula    is   loaded   with   pollen. 

British  Bee  Journal,  vol.  40,  pp.  144,  145,  Apr.  11. 
1912.— (c)   Pollen   collecting.      British   Bee   Journal,   vol.   40,   pp.    164-166, 

Apr.  25. 
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1912. —  (e)   Hind  legs  of  the  worker  honey  bee.     Canadian  Bee  Journal, 
vol.  20,  p.  203.     July. 
Wolff,  O.  J.  B.,  1873. — Das  Pollen-Einsammeln  der  Biene.     Eichstadt  Bienen  - 
Zeitung.    29  Jahrg.  Nrs.  22  u.  23,  pp.  258-270. 


INDEX. 


Page. 

Alefelb  on  pollen  moistening  by  worker  bee 23 

Antenna  cleaner  of  worker  bee,  figure S 

Auricle  of  hind  planta  of  worker  bee,  definition 9 

figure 11 

role  and  action  in   pollen  collect- 
ing  16-17,  19,  20-22 

Basket,  pollen.     (See  Corbicula.) 

Brush  of  foreleg  of  worker  bee,  action  and  role  in  pollen  collecting 13 

figure 8 

hind  leg  of  worker  bee,  action  and  role  in  pollen  collecting 16 

middle  leg  of  worker  bee,  action  and  role  in  pollen  collecting 14-16 

figure 9 

Brushes  of  legs  of  worker  bee,  use  in  pollen  collecting 8-9 

Bumblebee,  moistening  of  pollen,  views  of  Sladen 23-21 

Ches-hire  on  process  of  loading  pollen  baskets  by  worker  bee IT 

Comb  or  pecten  of  hind  tibia  of  worker  bee,  definition 0 

figure 77 

role  and  action  in  pollen  col- 
lecting    16-19 

Corbicula  of  worker  bee,  definition 9 

figure 10 

process  of  loading 15-22 

Corn,  sweet,  pollen  collecting  therefrom  by  honey  bee , 11-13 

Coxae  of  worker  bee,  figures S,  9 

Dunbar,  Dr.  P.  B.,  analyses  of  corn  pollen  from  plant,  from  corbiculaa 

of  bees,  and  from  hive  cells 28 

Femora  of  worker  bee,  figures 8,9,10,11 

Fleischmann  and  Zander  on  process  of  loading  pollen  baskets  by  worker 

bee ^ IS 

Flowers,  variable  amounts  of  pollen  from  different  plants 10-11 

Franz  on  pollen  moistening  of  worker  bee 23 

process  of  loading  pollen  baskets  by  worker  bee 17 

Hairs,  branched,  of  honey  bee,  use  in  pollen  collecting 7-S 

fringing  pollen  basket,  function 20 

unbranched,  of  honey  bee,  use  in  pollen  collecting 7,  8 

Hommell  on  pollen  moistening  of  worker  bee 23 

process  of  loading  pollen  baskets  by  worker  bee IS 

Honey,  use  by  worker  bee  for  moistening  pollen 24,28-29 

Leg,  hind,  of  worker  bee,  loaded  with  pollen,  figure 22 

Legs,  fore,  of  worker  bee,  action  and  role  in  pollen  collecting 12,33 

hind,  of  worker  bee,  action  and  role  in  pollen  collecting 13, 16-1S 

stages  in  basket-loading  process,  figure 19 

middle,  of  worker  bee,  action  and  role  in  pollen  collecting 13, 14-16 

of  worker  bee,  action  in  unloading  pollen 30-31 

structures  used  in  pollen  collecting- 7-9 

35 


36  BEHAVIOR   OE    HONEY   BEE   IN   POLLEN    COLLECTING. 

Page. 

Mandibles  of  honey  bee,  action  and  role  in  pollen  collecting 8,13 

worker  bee,  use  in  packing  pollen  in  the  cell 31 

Maxilke  of  honey  bee,  action  and  role  in  pollen  collecting 8,13 

Moistening  of  pollen  by  bumblebee,  views  of  Sladen 23-24 

honey  bee 13,22-29 

Mouthparts  of  honey  bee,  action  and  role  in  pollen  collecting 8, 13 

Nectar,  supposed  use  by  worker  bee  for  moistening  pollen 24-29 

Palma  of  foreleg  of  worker  bee,  definition 8 

Pecten  of  hind  tibia  of  worker  bee,  definition 9 

figure 11 

role  and  action  in  pollen  collecting 16-19 

Plauta  of  hind  leg  of  worker  bee,  definition 3 

figures 10, 11 

structures  concerned  in  pollen  collect- 
ing   9 

middle  leg  of  worker  bee,  definition 8 

Pollen,  chemical    composition 26 

collecting  by  worker  bee,  bibliography 33 

general  statement  regarding  it 11-13 

summary  of  process 31-32 

corn,  from  plant,  from  corbiculse  of  bees,  and  from  hive  cells, 

analyses  to  determine  nature  of  moistening  fluid 28-29 

moistening  by  bumblebee,  views  of  Sladen 23-24 

honey  bee 22-29 

storage  in  the  hive 29-31 

structures  of  honey  bee  concerned  in  manipulation 7-9 

supply  of  honey  bee 10-11 

unloading  process  by  worker  bee 30-31 

Saliva,  supposed  use  by  worker  bee  in  moistening  pollen 23,29 

Sladen,   observations  on  process   of  loading   pollen   baskets*  by   worker 

bee 18,  20,  21 

views  as  to  pollen  moistening  by  worker  bee 23-24,27 

Spur  of  middle  tibia  of  worker  bee,  figure 9 

Storing  pollen  in  the  hive 29-31 

Structures  of  honey  bee  concerned  in  manipulation  of  pollen 7-9 

"  Sweat  glands  "  of  Wolff  within  hind  tibia  and  planta  of  worker  bee. 

supposed  function 24 

Tibia  of  hind  leg  of  worker  bee,  modifications  and  structures  for  pollen 

collecting 9 

Tibiae  of  worker  bee,  figures 8,9,10,11 

Tongue  of  worker  bee,  action  and  role  in  pollen  collecting 8, 13 

Trochanters  of  worker  bee,  figures 8,  9 

Wax  shears  or  pinchers,  so-called,  use  in  loading  pollen  by  worker  bee 7 

Wolff  on  pollen  moistening  by  worker  bee 24 

Zander,  Fleischmann  and.     (See  Fleischmann  and  Zander.) 

o 


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